Viral encephalitides - Chem-Bio-Rad Suspicion
- Venezuelan equine encephalitis (VEE)
- Western equine encephalitis (WEE)
- Eastern equine encephalitis (EEE)
California encephalitis group
Although the vast majority of natural infections occur as a result of a bite from an infected mosquito, these viruses are also infectious as aerosols and, therefore, could possibly be utilized as a bioterrorism weapon. There is a report of transmission via blood transfusion.
VEE would be the most likely candidate for weaponization due to its stability and ability to be highly infectious at a low dose. It also produces nearly 100% symptomatic infections. In addition, it has the potential to be altered genetically to produce a more virulent strain. Any outbreak of viral encephalitides in non-endemic areas or without preceding equine cases should be highly suspect for a bioterrorism attack.
Whether acquired naturally or as a result of a bioterrorism event, symptoms of the viral encephalitides range from none to mild to severe and may include 24–72 hours of spiking fever, chills, fatigue, myalgias (especially in the low back), severe headache, and photophobia. Nausea, vomiting, sore throat, conjunctival redness, and diarrhea may quickly follow the initial onset of illness. The disease may progress to CNS disturbances such as seizures, ataxia, paralysis, paresis, delirium, coma, and death. Severe CNS involvement is more common in children.
The mortality rate of naturally occurring viral encephalitides is greater than 1% overall but may be as high as 20% after progression to severe encephalitis. However, mortality rates could be higher still following an aerosol bioterrorism attack due to a higher initial exposure and/or greater virulence through genetic manipulation. EEE causes the most severe arbovirus encephalitis and has a high mortality rate.
The incubation period of viral encephalitides is typically 1–6 days. Viral reservoirs include horses, bats, birds, rodents, donkeys, mules, and tropical mammals from which the virus is transmitted via mosquitoes to humans and equines. Person-to-person transmission may be possible but has not been proven.
Viral encephalitides are endemic to tropical regions of Central and South America, especially in rural areas. Eastern equine, western equine, St. Louis, and West Nile virus encephalitis are all endemic in North America.
Veterinarians, laboratory workers, tourists, military personnel, ranch workers, horseback riders, and residents of tropical areas are at higher risk for contracting viral encephalitides. Children are more susceptible to moderate or severe forms of the disease.
Note: Mosquito control is important to prevent both natural transmission and secondary cases after a bioterrorism attack. Prevent mosquito bites in endemic areas with insect repellant and proper clothing. Vaccinate equines with TC-83 (a live attenuated virus).
G05.3 – Encephalitis and encephalomyelitis in diseases classified elsewhere
34476008 – Viral encephalitis
- Viral encephalitides are often misdiagnosed as influenza in patients who have recently traveled in endemic areas. Dengue fever and malaria may present in a similar fashion and are also endemic to tropical areas.
- Yellow fever
- Bacterial and viral meningitis
- Brain abscess
- Subdural empyema
- Embolic encephalitis due to bacterial endocarditis
- Lyme disease
- Tuberculous meningitis
- Fungal meningitis
- Rocky Mountain spotted fever
- Cat-scratch disease
- Toxoplasmosis in the immunocompromised patient
- Typhoid and paratyphoid fevers
- Typhus (endemic and epidemic)
- Lupus cerebritis
- Cerebral vasculitis
- Lymphomatous cerebritis
- Nipah virus
- Kyasanur Forest disease